1. Field of the Invention:
The field of the invention is devices for the electropneumatic control of pneumatically operated mechanisms. More particularly, the field of the invention is such devices which operate to control high pressure industrial process pneumatic mechanisms over a broad range of pressure inputs (typically 0 to 100 psi).
2. Description of the Prior Art:
There are a wide variety of pneumatically operated devices in use today. These devices can generally be divided into two broad categories: low pressure devices and high pressure devices. Many Heating, Ventilating, and Air Conditioning systems (HVAC) include typical low pressure devices. Such devices operate on a range of 3-15 psi, and do not require fast response time or great accuracy. Many high pressure devices operate on a range of 0 to 100 psi and generally require high pressure inputs to move the larger mechanical mechanisms which they involve. Such devices include a wide range of industrial process applications. Although many such devices have not operated on high resolution input, there are significant attendant advantages to be gained by such operation. One area in which a fast actuating, high resolution input would be most useful is Robotics. Just one example where Robotics can effectively utilize a fast actuating, high resolution input is linear positioning.
There are three basic types of electropneumatic transducers in use to control industrial process pneumatic mechanisms: voice-coil beam; voice-coil beam damped by an oil dashpot; and torque motor mechanisms. Voice-coil beam transducers, which basically utilize a nozzle and flapper to generate a proportionate pneumatic signal in response to an electrical current which varies the position of the flapper with respect to the nozzle. Voice-coil beam transducers tend to be vibration sensitive and are thus not suitable for workpoint application. In a damped transducer, an oil dashpot reduces the sensitivity to vibration, however the response time is much slower and damped transducers are position sensitive since the oil can leak out. Torque-motor transducers utilize a torque motor to control the position of the flapper. These devices are relatively insensitive to vibration and mounting angle, however, they weigh up to 3 to 4 times as much as voice-coil units and cost 3 to 5 times as much. Because of their weight and cost, torque-motor transducers are often not suitable for workpoint pneumatic control either.
There is a need for a device which can quickly and accurately control pneumatically operated industrial process mechanisms over a broad range of pressures and which is insensitive to position or vibration.